1. Field of the Invention
This invention relates to a liquid crystal display, and more particularly to a hybrid backlight driving apparatus for a liquid crystal display wherein a high voltage can be converted into a driving voltage of a hybrid backlight to be supplied to lamps and light emitting diodes of the liquid crystal display.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) controls light transmittance of liquid crystal cells in accordance with video signals to thereby display a picture. An active matrix type liquid crystal display device having a switching device provided for each liquid crystal cell is advantageous for displaying moving pictures because it permits an active control of the switching device. The switching device used for the active matrix liquid crystal display device mainly employs a thin film transistor (TFT) as shown in FIG. 1.
Referring to FIG. 1, the active matrix LCD converts a digital input data into an analog data voltage on the basis of a gamma reference voltage to supply it to a data line DL and, at the same time, supplies a scanning pulse to a gate line GL to thereby charge a liquid crystal cell Clc.
A gate electrode of the TFT is connected to the gate line GL while a source electrode thereof is connected to the data line DL. Further, a drain electrode of the TFT is connected to a pixel electrode of the liquid crystal cell Clc and to one electrode of a storage capacitor Cst. A common electrode of the liquid crystal cell Clc is supplied with a common voltage Vcom.
The storage capacitor Cst plays a role in charging a data voltage fed from the data line DL when the TFT is turned on, thereby constantly keeping a voltage at the liquid crystal cell Clc.
If the scanning pulse is applied to the gate line GL, then the TFT is turned on to provide a channel between the source electrode and the drain electrode thereof, thereby supplying a voltage on the data line DL to the pixel electrode of the liquid crystal cell Clc. Therefore, liquid crystal molecules of the liquid crystal cell change the alignment direction due to an electric field between the pixel electrode and the common electrode to thereby modulate an incident light.
A configuration of the related art LCD including pixels having the above-mentioned structure will be described with reference to FIG. 2. FIG. 2 is a block diagram showing a configuration of a general liquid crystal display device. Referring to FIG. 2, a general liquid crystal display device 100 includes a liquid crystal display panel 110 provided with thin film transistors (TFTs) for driving the liquid crystal cell Clc at an intersection of data lines DL1 to DLm and gate lines GL1 to GLn crossing each other, a data driver 120 for supplying a data to the data lines DL1 to DLm of the liquid crystal display panel 110, a gate driver 130 for supplying a scanning pulse to the gate lines GL1 to GLn of the liquid crystal display panel 110, a gamma reference voltage generator 140 for generating a gamma reference voltage to supply it to the data driver 120, a backlight assembly 150 for irradiating a light onto the liquid crystal display panel 110, an inverter 160 for applying AC voltage and current to the backlight assembly 160, a common voltage generator 170 for generating a common voltage Vcom and supplying them to the common electrode of the liquid crystal cell Clc of the liquid crystal display panel 110, a gate driving voltage generator 180 for generating a gate high voltage VGH and a gate low voltage VGL and supplying them to the gate driver 130, and a timing controller 190 for controlling the data driver 120 and the gate driver 130.
The liquid crystal display panel 110 has a liquid crystal injected between two glass substrates. On the lower glass substrate of the liquid crystal display panel 110, the data lines DL1 to DLm and the gate lines GL1 to GLn perpendicularly cross each other. Each intersection between the data lines DL1 to DLm and the gate lines GL1 to GLn is provided with the TFT. The TFT supplies data on the data lines DL1 to DLm to the liquid crystal cell Clc in response to the scanning pulse. The gate electrode of the TFT is connected to the gate lines GL1 to GLn while the source electrode thereof is connected to the data line DL1 to DLm. Further, the drain electrode of the TFT is connected to the pixel electrode of the liquid crystal cell Clc and to the storage capacitor Cst.
The TFT is turned on in response to the applied scanning pulse, via the gate lines GL1 to GLn, to the gate terminal thereof. Upon turning-on of the TFT, the video data on the data lines DL1 to DLm are supplied to the pixel electrode of the liquid crystal cell Clc.
The data driver 120 supplies the data to the data lines DL1 to DLm in response to a data driving control signal DDC from the timing controller 190. Further, the data driver 120 samples and latches the digital video data RGB fed from the timing controller 190, and then converts the digital video data RGB into an analog data voltage capable of expressing a gray scale level at the liquid crystal cell Clc of the liquid crystal display panel 110 based on a gamma reference voltage from the gamma reference voltage generator 140, thereby supplying it to the data lines DL1 to DLm.
The gate driver 130 sequentially generates a scanning pulse, that is, a gate pulse in response to a gate driving control signal GDC and a gate shift clock GSC from the timing controller 190 and supplies them to the gate lines GL1 to GLn. The gate driver 130 determines a high level voltage and a low level voltage of the scanning pulse in accordance with the gate high voltage VGH and the gate low voltage VGL from the gate driving voltage generator 180.
The gamma reference voltage generator 140 receives a highest-level power voltage VDD supplied to the liquid crystal display panel 110 to thereby generate a positive gamma reference voltage and a negative gamma reference voltage, and outputs them to the data driver 120.
The backlight assembly 150 is provided at the rear side of the liquid crystal display panel 110, and is radiated by alternating current (AC) voltage and current supplied to the inverter 160 to irradiate a light onto each pixel of the liquid crystal display panel 110.
The inverter 160 converts a rectangular wave signal generated at the interior thereof into a triangular wave signal and then compares the triangular wave signal with a direct current (DC) power voltage Vcc supplied from said system, thereby generating a burst dimming signal proportional to a result of the comparison. If the burst dimming signal is determined in accordance with the rectangular wave signal at the interior of the inverter 160, then a driving integrated circuit (IC) for controlling the generation of the AC voltage and current within the inverter 160 controls the generation of AC voltage and current supplied to the backlight assembly 150 in response to the burst dimming signal.
The common voltage generator 170 receives a high-level power voltage VDD to generate a common voltage Vcom, and supplies it to the common electrode of the liquid crystal cell Clc provided at each pixel of the liquid crystal display panel 110.
The gate driving voltage generator 180 is supplied with a high-level power voltage VDD to generate the gate high voltage VGH and the gate low voltage VGL, and supplies them to the data driver 130. Herein, the gate driving voltage generator 180 generates a gate high voltage VGH higher than a threshold voltage of the TFT provided at each pixel of the liquid crystal display panel 110 and a gate low voltage VGL lower than the threshold voltage of the TFT. The gate high voltage VGH and the gate low voltage VGL generated in this manner are used for determining a high level voltage and a low level voltage of the scanning pulse generated by the gate driver 130, respectively.
The timing controller 190 supplies the digital video data RGB from a digital video card (not shown) to the data driver 120 and, at the same time, generates a data driving control signal DCC and a gate driving control signal GDC using horizontal/vertical synchronizing signals H and V in response to a clock signal CLK and supplies them to the data driver 120 and the gate driver 130, respectively. Herein, the data driving control signal DDC includes a source shift clock SSC, a source start pulse SSP, a polarity control signal POL and a source output enable signal SOE, etc. The gate driving control signal GDC includes a gate start pulse GSP and a gate output enable signal GOE, etc.
A related art backlight driving apparatus for driving a backlight of the liquid crystal display device having the above-mentioned configuration will be described with reference to FIG. 3 below. FIG. 3 shows a configuration of a backlight driving apparatus in the related art liquid crystal display device. Referring to FIG. 3, the backlight driving apparatus 200 includes a rectifier 210 for converting a commercial power voltage (e.g., alternating current (AC) voltage of 220V) into a direct current (DC) voltage, a smoother 220 for eliminating a ripple loaded on the DC voltage converted by the rectifier 210, a power factor corrector 230 for correcting a power factor of the DC voltage outputted from the smoother 220 and outputting a DC voltage of 400V, a DC/DC converter 240 for converting the DC voltage of 400V outputted from the power factor corrector 230 into a DC voltage of 24V to output it to the inverter 160, and an inverter 160 for converting and boosting the DC voltage of 24V inputted from the DC/DC converter 240 into an AC voltage of 1000 Vrms and supplying it to the backlight assembly 150.
Herein, the rectifier 210, the smoother 220, the power factor corrector 230 and the DC/DC converter 240 are provided at a power board (not shown) of a system such as a monitor, a television receiver or the like employing the liquid crystal display device 100 rather than at the liquid crystal display device 100. On the other hand, the inverter 160 is provided at the liquid crystal display device 100.
The related art backlight driving apparatus having the above-mentioned configuration has a problem in that it encounters an unnecessary power loss because the DC voltage of 400V outputted from the power factor corrector 230 is supplied to the inverter by way of the DC voltage conversion process made at the DC/DC converter 240 and in that it further reduces the voltage conversion efficiency because the inverter 160 converts and boosts the DC voltage of 24V into the AC voltage of 1000 Vrms.
Furthermore, the liquid crystal display device 100 provided with a hybrid backlight employs a boost converter to supply a driving voltage to a plurality of light emitting diodes (LEDs) (not shown). However, since such a boost converter has a deteriorated efficiency compared to a buck converter and requires many parts or elements, a driving efficiency of the plurality of LEDs is reduced and the manufacturing cost rises due to the need of many parts or elements.